[LLVMdev] Question about SSA-transformation
Fernando Magno Quintao Pereira
fernando at CS.UCLA.EDU
Sat Feb 17 14:51:12 PST 2007
Dear LLVM'ers,
I'm producing code for the PowerPC, and many often times it happens
that the bytecodes generated by LLVM have phi-functions like:
A4 = phi(A1, A2)
A5 = phi(A1, A3)
Where the 'A1' parameter appears in two different phi-functions. Could
someone give me an example in "pseudo-assembly" that would produce code
like that after being transformed into SSA form? Does it happen because of
some optimization, like in:
V = 1000;
if(...) {
A1 = 1;
A2 = 2;
} else {
A1 = V;
A2 = V;
}
use(A1);
use(A2);
Where one can remove the assignments that use 'V' by placing it directly
in the phi function, like in:
V = 1000;
if(...) {
A1 = 1;
A2 = 2;
}
A3 = phi(V, A1);
A4 = phi(V, A2);
Thanks,
Fernando
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